The Mount Tabor Reservoir No. 1 in Portland, Ore., one of four sites where water tested was found to be contaminated with E. coli, a type of bacteria found in feces. / Benjamin Brink, AP

by Cornelius Swart, KGW-TV, Portland, Ore.

by Cornelius Swart, KGW-TV, Portland, Ore.

PORTLAND, Ore. - The city's water department issued a boil-water order Friday for more than 650,000 residents of Oregon's largest city and several suburbs, telling people to toss ice from their ice makers, throw out previously made lemonade and not use tap water to brush their teeth.

In three tests from Tuesday to Friday, repeat water samples in four locations showed the presence of E. coli, a type of bacteria found in feces, and total coliform, bacteria commonly found in the environment but problematic in drinking water, officials said.

"The chance of any health problems related to this water test result is low. If any problems occur, we would expect diarrhea," said Dr. Paul Lewis, interim Tri-County health officer. "We monitor cases of bacterial diarrhea and will be aware of any increase following this event."

Even homes with water filters should heed the order because most water filters don't remove bacteria or viruses, according to the federal Centers for Disease Control and Prevention. Systems featuring hot water on demand also don't meet the requirements to fully boil water for at least one minute.

The city is investigating the source of the contamination, which can occur with a loss of water pressure, a pipe break or conditions that expose drinking water to outside elements.

The Portland Water Bureau said it collects about 240 water samples a month throughout its system, and the test to determine the presence of bacteria takes 18 hours.

One of the sites where E. coli-tainted water was discovered is Mount Tabor Reservoir No. 5, the spot last month where security cameras caught a man urinating through an iron fence into the open-air reservoir. Officials were going to discard all 38 million gallons in the reservoir but later decided to move it to an older concrete-lined holding area, Reservoir No. 6, which hasn't been used since 2010. It won't be used for drinking.

Though residents still can take showers and do laundry, the boil order, which is in effect until further notice, will affect both homes and businesses.

Water with dish soap can be used to clean cereal bowls but residents must rinse the bowls in boiled water and even wipe off the table with a towel moistened in boiled water. Fresh fruits and vegetables - any food that is not cooked afterward - must be washed in previously boiled water. And shut the automatic ice maker off; if someone wants ice, boil the water and put it in an ice-cube tray before freezing it.